U.S. Pat. No. 4,719,130 deals with a toner-fixer roll having an outer layer of a silicone rubber differing most obviously from that of the present invention in that the silicone contains no phenyl groups. The patent teaches the use of thermal stabilizers, and lists ten examples, at col. 3 lines 4-13. Included in this list is "cerium oxide." The thermal stabilizers are said to be useful for the purposes of that patent at 1 to 30 weight percent for the metal oxides. In Example 2, col. 5 line 55, there is shown a formulation which comprises "cerium oxide" in an amount which calculates out to be 0.024 weight percent. The patent is otherwise silent in regard to "cerium oxide," and makes no mention at all of the ceric dioxide which is required in the present invention.
U.S. Pat. No. 4,807,341 deals with a fusing roll having a coating of a copolymer having dimethylsiloxane and from 5 to 15 mole percent diphenylsiloxane recurring units. The patent discloses the use of a mixture of alumina and ferric oxide as a filler to strengthen the polymer.
U.S. Pat. No. 4,702,964 deals with a fixing roll containing a silicone rubber very different from that of the present invention. The patent makes mention of the addition of thermal conductivity increasing agents which may be graphite, metal, iron oxide, zinc oxide, boron nitride and the like, singly or mixed.
U.S. Patent application, Ser. No. 07/145,959, filed Jan. 20, 1988, and assigned to the same assignee as the present application, shows a fuser roller coating which comprises a poly (hydroxyether-diphenyldimethylsiloxane) copolymer. The application also discloses the use of a 56% zinc oxide, 7% graphite filler to improve thermal conductivity and mechanical properties of that elastomer.
Hot roll fusing is used in electrophotographic printing and copying to fix the toner on the paper. At higher printing speeds it is desirable to have the hot roll be softer than the back-up roll. This necessitates the use of a thermally conductive layer on the surface of the heated roll, which is simultaneously elastically deformable and thermally conductive. Many composite elastomer materials which provide these properties have been described in the literature. However, a major problem with all such materials is that they arc liable to abrasive wear due to contact with the paper. Thus they have limited life and must be replaced at regular intervals, adding significantly to the maintenance cost of the printer or copier. The present invention describes an elastomer formulation which exhibits significant improvements over previous material combinations.
In designing a hot roll fuser elastomer it is necessary to ensure functional properties of the material, namely compliance, thermal conductivity and toner release characteristics, while at the same time maximizing the lifetime abrasion resistance and thermal stability. Also, it is necessary to ensure that the material is processable into the final device at reasonable cost. The formulation described herein achieves all these objectives in a manner superior to any other described in the literature, or used in the art.